pub fn dp_rec_mc(amount: u32) -> u32 {
    let mut ret = 0;
    let mut total = amount;
    ret += total / 100;
    total %= 100;
    ret += total / 50;
    total %= 50;
    ret += total / 30;
    total %= 30;
    ret += total / 20;
    total %= 20;
    ret += total / 10;
    total %= 10;
    ret += total / 5;
    total %= 5;
    ret += total / 2;
    total %= 2;
    ret += total;
    println!("amount: {}, change: {}", amount, ret);
    ret
}
